High accuracy of measurement is required in levelling devices which are used, in particular, in building construction and civil engineering. In particular, in laser beam levelling devices where the laser beam issuing from the device is received at a relatively great distance by a receiver and is rendered visible so that large areas can be brought into the desired inclination, even small deviations of inclination on the device can lead to intolerably large faulty measurements in the receiver. As these devices are used in the open, they should also be insensitive to temperature variations.
In such devices, therefore, the operations of rendering horizontal and of inclining have been separated from one another. A movable measuring plate to which the laser plane is connected is located in the device. If the device is now erected on uneven terrain, the measuring plate is rendered horizontal by means of electrolytic levels. Electrolytic levels are filled, apart from a small gas bubble, with an electrically conductive liquid. One respective end of an electric conductor projects into the gas bubble from both sides. As soon as the level leaves the vertical, the electrical measured value changes owing to the displacement of the gas bubble and it is possible to determine that the level is no longer vertical and to which side it is inclined.
In order to incline the laser plane, a mechanical adjusting device is arranged between the measuring plate and the laser plane. This mechanism is very complicated, particularly if the laser plane is to be inclined in two axes which are at right angles to one another, and has to be produced with maximum precision.